Development of Emissions Factor for the Decentralized Domestic Wastewater Treatment for the National Greenhouse Gas Inventory Yoshitaka EBIE*, Hiroshi YAMAZAKI**, Shigeaki INAMURA***, Yusuke JIMBO*, Takuro KOBAYASHI*, Hiroyuki UEDA**** *Center for Material Cycles and Waste Management Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba-shi, Ibaraki 305-8506, Japan **Engineering Department, Ibaraki Pharmaceutical Association, 978-47 Kasahara, Mito-shi, Ibaraki 310-0034, Japan ***Iwate Johkasou Inspection Center, 3-5-8 Ryutsu-center minami, Yahaba-machi, Shiwa-gun, Iwate 020-0891, Japan ****Environment and Energy Department, Mitsubishi UFJ Research and Consulting, 5-11-2 Toranomon, Minato-ku, Tokyo 105-8501, Japan ABSTRACT Methane and N 2 O emissions were measured simultaneously in three s of decentralized wastewater treatment facilities to develop new emission factors (s) in Japan. Considering the ratio of the actual load to designed load and elapsed time from last desludging, 24 sites for Johkasou treating domestic wastewater, 6 sites for Johkasou treating night soil only, and 30 sites for vault toilet were selected. Gas samples were collected in the morning, afternoon, and evening for every Johkasou site. The investigation was conducted in summer and winter to estimate the annual average s. The s of CH 4 and N 2 O of both Johkasou were higher than that used in the national greenhouse gas inventory in 2012, whereas the CH 4 and N 2 O s of vault toilet were lower. Especially, N 2 O was only 1% of the national inventory in 2012, and almost zero. According to the results of these three s of decentralized wastewater treatment facilities, the emissions of CO 2 eq in FY2010 were 1.77 times higher than the national inventory. Keywords: greenhouse gas emission, inventory, Johkasou, vault toilet INTRODUCTION In Japan, approximately 20% of the population relies on decentralized systems to treat their domestic wastewater (MOEJ, 2013). Johkasou is a popular facility in sparse area. This system is most commonly composed of two anaerobic tanks and an aerobic tank. A portion of the influent organic carbon and nitrogen is converted to methane (CH 4 ) and nitrous oxide (N 2 O) in Johkasou. Because over 10 million people use this system (MOEJ, 2013), Johkasou is one of the significant sources of greenhouse gases (GHGs) emissions. which stores night soil is another major facility in the countryside. Collected night soil from vault toilet is treated in a plant that is set to treat night soil. The vault toilet also has a potential to emit GHGs during storage. The greenhouse gas emission factor () has been one of the important indicators of wastewater treatment technology in recent years. The s had been developed in the early 1990s (Tanaka, 1998), however, the investigation was not adequate and detailed methodology of the measurement was not described. Besides, revision of the technical guidelines for Johkasou of the Building Standards Act in 2001 had allowed makers to develop and sell new s of Johkasou which are approved based on performance certification. Then, a lot of new s of Johkasou were installed over the past 12 years Address correspondence to Yoshitaka Ebie, Center for Material Cycles and Waste Management Research, National Institute for Environmental Studies, Email: ebie.yoshitaka@nies.go.jp Received May 13, 2013, Accepted August 10, 2013. - 33 -
or so. The s of a lot of those Johkasou should be different from the old ones. The new process composed of anaerobic-aerobic circulation which is popular in the last decade is adopted for Johkasou treating domestic wastewater, and relatively low CH 4 and N 2 O emissions had been reported in this operational condition (Ebie et al., 2012). As for the vault toilet, s had been provisionally substituted by Johkasou treating night soil only because of the lack of data. Therefore, there is a possibility of deviation of national greenhouse gas inventory (MOEJ-GIO-CGER-NIES, 2012) from actual GHGs emissions in the sector of decentralized domestic wastewater treatment facilities. Here, direct measurements of the s of CH 4 and N 2 O from Johkasou treating domestic wastewater, Johkasou treating night soil only, and vault toilet are reported. MATERIALS AND METHODS Survey conditions A total of 24 sites for Johkasou treating domestic wastewater, 6 sites for Johkasou treating night soil only, and 30 sites for vault toilet were selected. All the investigations were done in winter (January and February 2012) and summer (July and August 2012) to estimate the annual average s. Survey sites of Johkasou treating domestic wastewater The investigation was focused on Johkasou treating domestic wastewater for 5 10 people. To prevent dependence, 6 s of Johkasou were selected considering installed number, recent number of sales, and diffusion potential in the future. These s of Johkasou can be categorized as national structure standard-compatible, BOD removal, and BOD and T-N removal. For each, 4 sites were selected based on the conditions mentioned in Table 1 to avoid bias, although the effects of these factors on greenhouse gas emission were not clear. The ratio of actual load to designed load was estimated by the ratio of the actual number of occupants to the designed number of occupants. The elapsed time from the last desludging was confirmed with desludging service company. All the sites were numbered consecutively with heading G; for example G-1, G-2, and G-3. Only G-11 was missing because occupant s consent to the on-site investigation could not be obtained. A PVC gas sampling pipe was set at wastewater catch basin after sealing up all the manhole covers and capping the effluent pipe (Fig. 1). The gas sample was collected in a gas bag (AAK-1, GL Science, Tokyo) by the use of air pump (MP-Ʃ100HN, SIBATA, Tokyo). The flow rate of the air pump was set at 1.0 L/min. Normally, the air blower capacity of Johkasou for 5 people is over 60 L/min, and 1.0 L/min of air pump is adequately low flow rate. Gas samples were collected in the morning, afternoon, and evening for every site. Atmospheric gas was collected for comparison as a baseline air. The actual air flow of blower was measured in each site to calculate the amount of CH 4 and N 2 O emissions. Survey sites of Johkasou treating night soil only A contact aeration with pre-sedimentation process was selected because it is a popular of Johkasou treating night soil only. The structure and the performance are not so different from each product of Johkasou treating night soil only. Survey site selection - 34 -
Table 1 - Survey site selection conditions for each of Johkasou. Parameters Condition 1 Condition 2 Ratio of actual number of occupants to designed number of occupants not greater than 0.5 more than 0.5 Elapsed time from last desludging not greater than half year more than half year *Desludging shall be done within a year by Johkasou law. Fig. 1 - Diagram of the sampling technique developed for Johkasou treating domestic wastewater. conditions and gas sampling method were the same with the Johkasou treating domestic wastewater. All the sites were numbered consecutively from T-1 to T-6. Survey sites of vault toilet Two s of vault toilets, with and without a small amount of water flushing device, were investigated. The house which installed two or more toilet was excluded in this study. Survey sites for the vault toilet without water flushing device were numbered consecutively from M-1 to M-17. Survey sites for vault toilet with a small amount of water flushing device were numbered consecutively from K-1 to K-16. Because occupant s consent to the on-site investigation could not be obtained, M-6, M-11 and K-12 were missing. A PVC flux chamber (25 and 25.5 m in diameter and height, respectively) was constructed. A suction port and a vent port were located at the top of the flux chamber. The flux chamber was lowered directly into the liquid surface. An air pump (MP-Ʃ100HN, SIBATA, Tokyo) was connected to the suction port and the flow rate was set at 1.0 L/min to equilibrate the rate of GHGs emission and the rate of dilution by the air outside (Fig. 2). At least two hours later, the gas sample was collected in a gas bag 4 times every 5 minutes. Atmospheric gas was also collected for comparison as a baseline air. Gas analysis Concentrations of CH 4 and N 2 O in the collected gas samples were determined using Shimadzu gas chromatograph (GC-8A, Shimadzu Co., Tokyo) with flame ionization detector or 63 Ni electron capture detector. - 35 -
Air inlet Vent port Suction port Flux chamber Air pump Gas bag Fig. 2 - Diagram of the sampling technique developed for vault toilet. RESULTS AND DISCUSSION GHGs emission from Johkasou treating domestic wastewater The gas concentrations of the samples and air flow of the blower measured on site were multiplied and divided by the number of the occupants for each survey site. Average CH 4 and N 2 O concentrations in the gases collected in the morning, afternoon, and evening for every site were used for the calculation of s of CH 4 and N 2 O (Tables 2 and 3). Because many parameters such as influent pattern, water temperature, quality and quantity of domestic wastewater vary from house to house, it is suggested that there is a big difference in gas emission in each site. Therefore, varied GHGs emission in each site should be recognized as actual conditions. Average s of CH 4 and N 2 O in each category and were also quite different. These results showed the importance of the category or the of Johkasou for GHGs emission. It makes sense to use these s for each category or of Johkasou in national inventory, however, the number of users for each category or, which is indispensable for the calculation of total GHGs emission, cannot be collected. Therefore, average values were determined as s of Johkasou treating domestic wastewater. Although much lower CH 4 emissions have been reported (Inamura, 2011), simplified on-site measurement was conducted by the use of a handy meter. Instead of sealing the manhole and capping the effluent pipe, the manhole cover was opened a little and the inlet of the handy meter was inserted from the gap. Then, emitted gases from Johkasou might be mixed with a certain amount of ambient air. Emission factors used in national inventory should be estimated conservatively and underestimation must be avoided. Sampling and measurement methods in this study have been developed based on this experiment. Both CH 4 and N 2 O emissions depend on microbial activity which is affected by temperature. In this study, higher CH 4 s were observed in summer in all categories. However, no clear correlation was confirmed between N 2 O and season. While CH 4 is the final product of anaerobic metabolite, N 2 O is the intermediate metabolite in nitrification and denitrification processes (Ritchie and Nicholas, 1972; Knowles, 1982). The influence of temperature is different between nitrification and denitrification processes (Ilies and Mavinic, 2001). When high efficiency of nitrification and - 36 -
denitrification is achieved, N 2 O production would be low. However, quite low ammonia oxidation rate also leads to low N 2 O generation. Therefore, different Johkasou category should have a different degree of temperature effects on N 2 O generation. Furthermore, the solubility of N 2 O is quite high compared with CH 4, and the temperature is an important factor of gas solubility (Weiss and Price, 1980). These complexities of N 2 O emission might be one of the reasons for the different seasonal tendency of N 2 O s in each category. Table 2 - Emission factors of CH 4 from Johkasou treating domestic wastewater. Category Type Category A: Type A: National National structure structure standardscompatible compatible standards- Type B: Compact Category B: BOD removal Type C: Preaeratoin Category C: BOD and T-N removal Type D: Advanced Type E: Advanced Type F: Advanced Certified Winter Summer Annual average effluent water No. in in in in in in in in quality site category site category category G-5 4,471 7,995 BOD 20 mg/l G-6 137 3,136 1,385 1,385 G-7 201 845 3,568 3,568 2,477 2,477 G-8 732 2,294 G-9 2,214 2,757 G-10 4,123 BOD 20 mg/l G-12 1,042 2,190 1,661 2,764 2,477 G-25 1,383 2,858 G-26 1,568 3,779 2,400 1,984 G-13 1,887 3,418 BOD 20 mg/l G-14 141 1,303 945 G-15 1,648 2,365 2,036 1,490 G-16 102 1,101 1,057 2,569 1,835 G-1 121 8,047 G-2 103 1,963 98 G-3 14 62 2,611 1,355 BOD 20 mg/l, G-4 156 372 T-N 20 mg/l G-17 32 1,820 G-18 73 1,825 276 349 G-19 166 165 1,256 1,739 766 1,044 G-20 831 1,212 G-21 757 1,858 BOD 10 mg/l, G-22 349 1,934 674 T-N 10 mg/l G-23 644 365 1,351 1,013 G-24 948 1,244 Unit: gch 4/person/year Table 3- Emission factors of N 2 O from Johkasou treating domestic wastewater. Category Type Category A: Type A: National National structure structure standardscompatible compatible standards- Type B: Compact Category B: BOD removal Type C: Preaeratoin Category C: BOD and T-N removal Type D: Advanced Type E: Advanced Type F: Advanced Certified Winter Summer Annual average effluent water No. in in in in in in in in quality site category site category category G-5 0.1 137.7 BOD 20 mg/l G-6 39.7 95.7 41.1 41.1 G-7 73.1 165.3 102.4 102.4 71.7 71.7 G-8 51.3 10.7 G-9 86.6 34.2 G-10 34.0 BOD 20 mg/l G-12 62.6 53.8 16.8 24.7 39.3 G-25 32.1 31.1 G-26 55.7 16.6 53.3 54.5 G-13 18.7 219.4 BOD 20 mg/l G-14 61.1 67.2 57.6 G-15 52.1 3.3 81.9 69.7 G-16 98.6 90.5 37.7 75.8 83.1 G-1 374.2 6.6 G-2 113.5 63.0 391.4 G-3 934.8 21.4 38.7 215.1 BOD 20 mg/l, G-4 143.3 63.9 T-N 20 mg/l G-17 164.0 357.8 G-18 25.4 56.5 81.1 174.8 G-19 75.9 10.7 134.5 71.7 107.8 123.2 G-20 59.2 112.9 G-21 39.1 6.1 BOD 10 mg/l, G-22 29.2 12.4 51.9 T-N 10 mg/l G-23 21.2 97.7 41.8 46.8 G-24 117.9 50.8 Unit: gn 2O/person/year - 37 -
Different s of Johkasou have different s of CH 4 and N 2 O. Lower CH 4 s were observed in BOD removal, and BOD and T-N removal of Johkasou showed the lowest one. A reduction effect of anaerobic-aerobic circulation on CH 4 emission has been reported (Ebie et al., 2012). The national structure-standards compatible of Johkasou does not have enough anaerobic-aerobic circulation process for nitrogen removal. This might be a reason of low CH 4 in BOD and T-N removal of Johkasou. Conversely, N 2 O of BOD and T-N removal of Johkasou was two times higher than that of BOD removal. This result suggests N 2 O generation in nitrification and denitrification processes. GHGs emission from Johkasou treating night soil only Emission factors of Johkasou treating night soil only were calculated by the same method for Johkasou treating domestic wastewater (Table 4). Higher CH 4 and N 2 O s were observed in summer in every site except in T-4. Because there is no anaerobic-aerobic circulation in these Johkasou, most of the N 2 O gas must be generated in the nitrification process. GHGs emission from vault toilet Average CH 4 and N 2 O concentrations of the samples collected in the site and air flow of the sampling pump were multiplied and divided by the number of occupants for each survey site. Emission factor was considered zero if it was calculated as a negative value (Tables 5 and 6). The vault toilet is not used for treatment but is used for storage of night soil. There is no aeration and agitation in the basin, and there is no opportunity to generate N 2 O during storage. However, N 2 O of vault toilet has been substituted by that of Johkasou treating night soil only because of lack of data. In this study, almost no emissions from vault toilet were confirmed by direct measurement investigation. Quite high CH 4 s were observed in summer whereas those in winter were very low. Average water temperatures in winter and summer were 3.7 and 23.0 C, respectively. It is suggested that this low temperature in winter affected methanogens and suppressed methane fermentation in the vault toilet. Table 4 - Emission factors of CH 4 and N 2 O from Johkasou treating night soil only. CH 4 N 2O No. Winter Summer Annual Annual Winter Summer average average in site in site in site in site T-1 483 2,368 4.8 13.0 T-2 1 983 6.3 12.9 T-3 13 217 0.3 182.2 110 810 460 22.8 T-4 98 191 121.7 17.8 55.5 39.1 T-5 42 815 2.3 97.9 T-6 23 285 1.0 9.3 Unit: g/person/year - 38 -
Category without a small amount of water flushing device with a small amount of water flushing device Category without a small amount of water flushing device with a small amount of water flushing device Journal of Water and Environment Technology, Vol.12, No.1, 2014 Table 5 - Emission factors of CH 4 from vault toilet. No. Winter Summer Annual average in site in category in site in category in category M-1 3.4 72.0 M-2 0.5 96.1 M-3 25.6 329.4 M-4 8.2 70.9 M-5 7.1 M-7 1.6 3.0 M-8 9.1 295.3 M-9 7.6 14.2 135.4 71.5 M-10 0.5 86.2 M-12 7.9 M-13 9.9 163.1 M-14 0.0 M-15 0.1 317.1 M-16 M-17 25.3 42.1 6.2 K-1 9.6 21.6 117.4 61.8 K-2 0.0 1.6 K-3 1.2 15.3 K-4 0.6 109.8 K-5 6.8 3.9 K-6 0.0 K-7 13.1 51.2 K-8 5.0 4.7 215.9 99.4 52.1 K-9 0.5 477.2 K-10 2.0 75.2 K-11 0.4 K-13 0.1 1.5 K-14 0.3 37.9 K-15 31.5 177.2 K-16 0.2 104.2 Unit: gch 4/person/year Table 6 - Emission factors of N 2 O from vault toilet. No. Winter Summer Annual average in site in category in site in category in category M-1 0.0 0.038 M-2 0.005 0.0 M-3 0.0 0.058 M-4 0.0 0.023 M-5 0.0 0.0 M-7 0.0 0.011 M-8 0.019 0.0 M-9 0.0 0.020 0.0 0.0100 0.0147 M-10 0.0 0.0 M-12 0.177 0.0 M-13 0.0 0.0 M-14 0.0 M-15 0.0 0.0 M-16 0.004 M-17 0.072 0.006 0.010 K-1 0.0 0.0 0.0329 0.0216 K-2 0.0 0.0 K-3 0.0 0.0 K-4 0.019 0.341 K-5 0.0 0.004 K-6 0.0 K-7 0.0 0.0 K-8 0.0 0.0012 0.0 0.0558 0.0285 K-9 0.0 0.056 K-10 0.0 0.104 K-11 0.0 K-13 0.0 0.161 K-14 0.0 0.059 K-15 0.0 0.0 K-16 0.0 0.0 Unit: gn 2O/person/year - 39 -
Emission factors of CH 4 and N 2 O Average of winter and summer s of CH 4 and N 2 O were decided as annual s (Table 7). The CO 2 equivalent emissions were converted by using global warming potential indexed multipliers of 21 and 310 for converting CH 4 and N 2 O, respectively. For Johkasou treating domestic wastewater, s were suggested for two different periods (before and after FY2001) due to the fact that the technical guidelines for Johkasou of the Building Standards Act were revised in this year, and the installation of performance certified Johkasou was started. For the period FY1990 2001, the s for national structure standards-compatible Johkasou would be used. For the period from FY2002 and onward, the average s for national structure standards-compatible Johkasou and performance certified Johkasou (BOD removal and BOD and nitrogen removal ) would be used. Annual trends in GHGs emission were calculated based on the new s developed in this study (Fig. 3). Because two different s were adopted for Johkasou treating domestic wastewater, emissions from Johkasou decreased in FY2002 even though the number of users increased. The differences of national inventory and this study in terms of CO 2 eq emissions are +463, +160, and 90 GgCO 2 for Johkasou treating domestic wastewater, Johkasou treating night soil only, and vault toilet, respectively. Then, the total emissions of CO 2 eq from these facilities in FY2010 were 1.77 times higher than the national inventory. Table7 - Summary of GHGs emission and the total gas emissions in terms of CO 2 equivalents. decentralized wastewater treatment facilities Johkasou treating domestic wastewater Johkasou treating night soil only CH 4 (gch 4/person/year) N 2O (gn 2O/person/year) CO 2eq (kgco 2/person/year) National Inventory 1,106 26 31.3 this study (FY1990-2002) 2,477 71.7 74.2 this study (from FY2002) 1,835 83.1 64.3 National Inventory 197 20 10.3 this study 460 39 21.8 National Inventory 197 20 10.3 this study 62 0.022 1.3 CO 2 eq (GgCO 2 ) 1,400 1,200 1,000 800 600 400 200 (A) Johkasou treating domestic wastewater Johkasou treating night soil only Total 0 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 0 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 Fig. 3 - Annual trends in GHGs emission with s of national inventory (A) and with s obtained in this study (B). CO 2 eq (GgCO 2 ) (B) 1,600 1,400 1,200 1,000 800 600 400 200 Johkasou treating domestic wastewater Johkasou treating night soil only Total - 40 -
CONCLUSIONS This study developed new emission factors (s) of CH 4 and N 2 O for three s of decentralized wastewater treatment facilities, Johkasou treating domestic wastewater, Johkasou treating night soil only, and vault toilet in Japan. Although the investigation of 24 sites for Johkasou treating domestic wastewater, 6 sites for Johkasou treating night soil only, and 30 sites for vault toilet showed a wide range of s in each site, the condition of survey site and target were well considered to reflect the actual and annual s of CH 4 and N 2 O. Characterization of GHGs emissions in detail is our future work for the technological development of CH 4 and N 2 O reduction. ACKNOWLEDGEMENT The authors acknowledge financial support from the Ministry of the Environment. Special appreciation is extended to the teams of Shiwa Town, Shiwa Johkasou Ltd., and Suuri-Keikaku Co., Ltd. RERENCES Ebie Y., Yamazaki H., Ogura Y. and Xu K. Q. (2012) Effect of influent fluctuation and anaerobic-aerobic circulation on CH 4 and N 2 O emissions in Johkasou. J. Jpn. Soc. Water Environ., 35(2), 27-32. (in Japanese) Ilies P. and Mavinic D. S. (2001) The effect of decreased ambient temperature on the biological nitrification and denitrification of a high ammonia landfill leachate. Water Res., 35(8), 2065-2072. Inamura S. (2011) Estimation of emission of methane, a greenhouse gas, from small-scale Johkasou using a portable gas detector. Johukasou Kenkyu, 23(2), 1-8. (in Japanese) Knowles R. (1982) Denitrification. Microbiol. Rev., 46(1), 43-70. MOEJ (2013) Pervasion of wastewater treatment at the end of FY2011. Ministry of the Environment Japan, Tokyo, Japan. (in Japanese) MOEJ-GIO-CGER-NIES (2012) National GHGs inventory report of Japan, Ministry of the Environment Japan/Greenhouse Inventory Office of Japan/Center for Global Environmental Research/National Institute for Environmental Studies, Tokyo/Tsukuba, Japan. Ritchie G. A. F. and Nicholas D. J. D. (1972) Identification of the sources of nitrous oxide produced by oxidative and reductive processes in Nitrosomonas europaea. Biochem. J., 126, 1181-1191. Tanaka M. (1998) Waste management and global environment. In: Outline of waste management, M. Tanaka (ed.), Japan Environmental Measurement and Chemical Analysis Association, Tokyo, p.339. (in Japanese) Weiss R. F. and Price B. A. (1980) Nitrous oxide solubility in water and seawater. Mar. Chem., 8(4), 347-359. - 41 -